Need help with Big Sur downgrade to Catalina

Before you upgraded to Big Sur did you make a full backup of your mac.

If so you can erase your mac and restore that full back up to your mac.

If you did not backup your mac before upgrading then you will need

to follow the procedure below. Make a full backup of your mac now.

Download macOS Catalina by opening your Safari browser

and clicking on this link,

How to get old versions of macOS – Apple Support

Go to Download OS and click on macOS Catalina.

This should redirect you to the App Store Catalina download page,

it should say Get or Download.

Once it has downloaded Install macOS Catalina.app, it will be in your

Applications folder you can then make a bootable USB installer using these

instructions, How to create a bootable installer for macOS – Apple Support

Boot to the USB installer, use Disk Utility to erase your Disk,

click View in the menubar and select Show All Devices,

highlight the Disk (probably called Apple SSD .........) not any of the indented

Volumes, click Erase, press Continue.

Give the Disk a name.

Format: APFS

Scheme: GUID Format Partition Map

Click Erase

When Done quit Disk Utility.

Click on Install OS, the installer will start follow the prompts.

When you have installed Catalina on your mac then you can Restore your personal data

back from the backup you made prior to erasing your mac.

Do not restore any system or library files or apps as these will put Big Sur

and Big Sur apps back on your mac.

So only your personal data.

Some files that you created or edited whilst using Big Sur may not be readable by

the apps in Catalina. Files created, edited and saved on a newer version of macOS

are often not backwards compatible.